{
  "eventId": "GRB 250603A",
  "subject": "GRB 250603A: Swift detection of a burst or new Galactic transient Swift J0839.7-3916",
  "createdOn": 1748915465097,
  "submittedHow": "email",
  "bibcode": "2025GCN.40613....1P",
  "body": "T. M. Parsotan (GSFC), R. Brivio (INAF-OAB), R. Gupta (NASA GSFC),\nM. J. Moss (GSFC), D. M. Palmer (LANL) and C. Salvaggio (INAF-OAB)\nreport on behalf of the Neil Gehrels Swift Observatory Team:\n\nAt 01:10:23 UT, the Swift Burst Alert Telescope (BAT) triggered and\nlocated GRB 250603A (trigger=1320335).  Swift slewed immediately to the burst.\nThe BAT on-board calculated location is \nRA, Dec 129.918, -39.268 which is \n   RA(J2000) = 08h 39m 40s\n   Dec(J2000) = -39d 16' 05\"\nwith an uncertainty of 3 arcmin (radius, 90% containment, including \nsystematic uncertainty).  The BAT light curve showed a complex\nstructure with a duration of about 18 sec with a possible short \nspike at T0+16 sec.  The peak count rate was ~1,300 counts/sec \n(15-350 keV), at ~1 sec after the trigger.\n\nThe XRT began observing the field at 01:12:04.7 UT, 101.7 seconds after\nthe BAT trigger. No source was detected in the 2.5-s promptly available\nimage. We are waiting for the full dataset to detect and localise the\nXRT counterpart.\n\nAlthough the initial 2.5s of XRT data do not show a clear X-ray\nafterglow, the high significance of the BAT image (7.82 sigma)\ngives us confidence that this is an astrophysical source.\nFurther analysis awaits the full downlinked dataset.\n\nWe note the presence of Fermi-GBM event at ~T+10 minutes\n(GBM trigger: 770606412) with a position consistent (to its\n25° error radius) with this source location.\n\nGiven the location of the BAT detection at 1.42° from the Galactic\nplane, persistent flux over 10 minutes would suggest a Galactic transient.\nIf so, we would name it Swift J0839.7-3916 .\n\nBurst Advocate for this burst is T. M. Parsotan (tyler.parsotan AT nasa.gov).\nPlease contact the BA by email if you require additional information\nregarding Swift followup of this burst. In extremely urgent cases, after\ntrying the Burst Advocate, you can contact the Swift PI by phone (see\nSwift TOO web site for information: http://www.swift.psu.edu/)\n\n",
  "submitter": "David Palmer at LANL <palmer@lanl.gov>",
  "circularId": 40613
}